While it is clear that the structures of the medial temporal lobe (MTL) are essential for our ability to learn and retrain new information for facts, events and relationships, the specific contributions of individual MTL structures to learning and memory remain poorly understood. The goal of this proposal is to take advantage of the precise spatial and temporal resolution of behavioral neurophysiology in the non-human primate to characterize the specific contributions of individual MTL areas and their interactions to various MTL-dependent tasks. In Aim 1, we will use a conditional motor association learning task known to be sensitive to MTL damage, to characterize the task-related and learning related signals in both the entorhinal and parahippocampal cortices using single and multiple tetrode recordings. We will interpret our findings in the context of our previous studies describing the associative learning signals in both in the hippocampus and perirhinal cortex during performance of the same associative learning task. Using variants of the conditional motor association task that emphasize either encoding, requiring pattern separation or recall, requiring pattern completion, we will test the hypothesis that area CA3 of the hippocampus may be most strongly or most quickly engaged in both encoding and recall versions of the task compared to area CA1 or the entorhinal cortex. Single and multi-tetrode recordings done throughout these experiments will allow us for the first time to characterize the correlated activity both within individual areas as well as across areas during new associative learning. In Aim 2 we will also use the computations of pattern completion and pattern separation to differentiate the functions of individual MTL areas using an incidental looking task analogous to incidental spatial/contextual encoding tasks used in rats. Understanding the functions and functional interactions of individual MTL structures has important implications for the development of treatments for the wide variety of disease states that affect memory including Alzheimer's disease, schizophrenia, attention deficit disorder as well as the memory impairments present in aging. Alzheimer's disease, schizophrenia, developmental disorders and aging all involve impairments in learning and memory associated with damage to the medial temporal lobe. Here we propose to use neurophysiological recording techniques to characterize the individual contributions and interactions of the key medial temporal lobe areas important for memory. This information will serve as an important foundation for the development of treatments for disorders of memory that affect the medial temporal lobe.